Also, is it considered ergonomically correct to rest one's elbows on the armrests of an office chair to help keep the hands above the keyboard with the wrists straightened?
I haven't seen any studies on the long term use of armrests, nor would I likely trust them, but I've been using modified armrests for about 4 years with great success.
There are at least 3 things necessary for comfortable armrest use:
1. Soft armrests. I tossed the stock, removable armrests and replaced them with oversized, super-padded ones.
2. Adjustable armrests. The armrests height, relative to your seat, must be right or they will ineffective.
3. The keyboard height. I use a keyboard tray to position the keyboard in the most natural position. The tray isn't necessary but the keyboard's position relative to your chair is.
Armrests are like most ergo practices; very subjective. When I moved my office location a few months ago, I used a chair without armrests for the about a month. My speed and accuracy went down dramatically and typing was much less comfortable. I realized then just how much I rely on them.